Correct - there is no code requirement for routine replacement of smoke detectors in commercial fire alarm systems.
However there are code requirements for annual functional testing and periodic sensitivity testing.
Correct - conventional smoke detectors do have a sensitivity increase over time. Some of this can be due to normal component aging but most is due to accumulation of dust and dirt as the picture below shows. Many commercial smoke detectors can be cleaned if they become a problem.
Not correct - the sensitivity increase does not contribute to false alarms. Making a smoke detector more sensitive does give a greater chance that a minor increase in obscuration in the sensing chamber will result in an alarm because of the dust and dirt already in the chamber.
